Leaking fuel selector - advice/tips on disassembly?

[Vance Harral]

Scrubbed a flight today due to discovery of a fuel leak around the fuel tank selector/strainer.  Got a whiff of fuel on opening the cabin, and discovered a large drop of fuel and a blue stain on top of the strainer stem in the cabin.  On looking under the belly, found obvious signs of leaking: blue stains on the strainer drain and nearby panels.  Pulled the belly panel and found more blue staining on and near the selector (photos below).

I'll be working with our local mechanic on the problem tomorrow, but wanted to solicit advice from anyone who's dealt with this.  An article on Don Maxwell's site says, "Fuel selector valve leaks are evident by stains around the fuel selector stem. In most cases these leaks are repaired by disassembling the selector and replacing the O-rings."  A prior thread on Mooneyspace discusses having LASAR rebuild the selector, or ordering a rebuild kit from LASAR or Don Maxwell.  But that same thread suggests there are multiple causes of leaks, some simpler to fix than others.

I've removed the sediment bowl and checked the screen during owner-assisted annuals in the past, including replacing the O-rings there.  But I've never removed or disassembled the selector itself, and not sure what other seals might be further inside.  My mechanic says he's never pulled the strainer stem in a Mooney, so it's going to be a new experience for both of us.  Any advice on what to look for?  I'm not opposed to sending the whole thing off to LASAR for overhaul, but we haven't had any of the trouble that typically leads to an overhaul, e.g. difficulty turning the selector valve or pulling the strainer.  Just this newly discovered leak.  If it's a simple matter of replacing a standard O-ring, that seems preferable to an overhaul.  Comments and advice appreciated.

[KSMooniac]

You might get it out and apart on a clean bench, and then call LASAR for parts and advice. It still might be wise to send it to them once you see what needs repair.

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[1964-M20E]

don't forget you need to empty the tanks before removing it.  I know captain obvious  here but worth a reminder.

 

I have not completely disassembled one before but I imagine withe a diagram and the proper o rings it should not be difficult for you and you mechanic.

 

 

 

 

[Vance Harral]

57 minutes ago, 1964-M20E said:

don't forget you need to empty the tanks before removing it.

Actually, I was hoping to avoid that if possible.  I'm aware fuel will stream out once the source lines are disconnected from the selector, but was hoping there's a way to plug the lines with just a small amount of fuel loss.  Completely draining the tanks would be a pain.  Tips anyone?

[mike_elliott]

10 hours ago, Vance Harral said:

But I've never removed or disassembled the selector itself, and not sure what other seals might be further inside.  My mechanic says he's never pulled the strainer stem in a Mooney, so it's going to be a new experience for both of us

Vance, this is one of those "I'll kill you if you don't fix me right" items. Personally, I wouldn't be on a learning curve here, unless you had a knowledgeable A$P rebuild it on site. It might pay just to send it off to Don or LASAR to get it OH'd and know it is right. Your call, your butt, your wallet, Your mileage

[deanders]

I removed mine and rebuilt it. You'll find you need to drain ALL the fuel from the tanks. It's very tight to get the lines off and removed, if you haven't emptied the fuel before, they will be empty by the time the selector is out. The rebuild isn't tuff but there are small balls and springs for the detents that are easy to loose.

[RLCarter]

Draining the tanks isn't that bad, you just need a clean container(s) for the fuel and a way to get the fuel back in the aircraft. I used the electric boost pump as per the service manual when doing a fresh weight & balance on mine. They make "AN" plugs for the "B Nuts", just remember you'll be laying on your back and reaching up to work which means 100LL will be running down your arm untill you get the flow stopped. I've had a Cessna 172 valve apart (O-rings, Springs and Ck Balls) but never a Mooney but would imagine it's about the same.

[Vance Harral]

Thanks for the advice, all.  In the usual way of "the broken appliance doesn't malfunction for the repairman", we're unable to see any leaking this morning. :-|

This of course doesn't mean the unit doesn't need a rebuild, but it could also mean the strainer pull shaft simply got slightly stuck open on the last preflight.

Advice from the mechanic is to let it sit a while and see if the staining returns.  Letting it sit on the ground a few days is a pretty low-risk maneuver while we mull over our options.

[Guest]

Be very careful draining your fuel tanks and working with lines containing fuel.  100LL is highly flammable, I have experienced a fire in the shop due to spilled fuel.  

To experience it first hand pour a few ounces of fuel in a cookie pan outside and throw a match at it, you'll be amazed.  I do this regularly to show my apprentices just how bad it is.

Clarence

[N201MKTurbo]

I just undo the lines and screw in a cap plug. You lose about a teaspoonful of fuel.

[Vance Harral]

For the sake of closure... I satisfyingly/unsatisfyingly report the fuel selector has not resumed its leak in the last week, including through a couple of cautious flights kept to the vicinity of airports.  Everyone's best guess is the strainer simply didn't seat properly at one point, either due to a small piece of debris which has been flushed out, or a slight "edge" in the mechanism somewhere that has been scraped smooth or just usually doesn't catch the moving parts.   If the latter, the problem may return.  But the risk of doing nothing at this time seems less than the risk of a maintenance induced failure R&Ring a critical part which is not actually failing in any observable way at this time.

[Bob_Belville]

I'm just reading this thread. We removed and disassembled mine selector at last annual. We did not drain tanks, Lynn plugged each line as disconnected. 

In my case the symptom was not a visible fuel leak but an erratic fuel flow gauge. JPI had me put a couple of drops of oil on the stem of the selector which fixed the problem - temporarily. What was going on was that air was being sucked into the fuel line @ the selector. A little air in the fuel line really fakes out the FF turbine.

Your mechanic should have no problem sourcing the o-rings, washers and the metal/rubber compression "washer" whose name I forget.

[cliffy]

Disassemble it on a clean white towel so if you forget (DON'T FORGET) about the 2 little ball bearings and springs they will be on the towel and not bouncing along the floor somewhere where you won't find them. Make sure you use a smooth brass pry tool on the shaft oring to avoid marring the aluminum housing. 

[M20C69]

right tank will not drain via selector valve, left tank does drain fine, off position terminates engine running. engine runs fine with selector in either left or right tank selection. selector handle works fine (apparently) 1969 m20c.  any ideas??

[M20C69]

CORRECTION; fuel selector drains only with bottom portion of selector valve and screen removed. screen appears u

n-plugged but ,,, i know nothing.